Simple machines

Simple machines are an engaging way to introduce Physical World science concepts.

A simple machine is a mechanical device that changes the direction or magnitude of a force.

A simple machine uses a single applied force to do work against a single load force.

Simple machines most commonly refer to:

• lever
• pulley
• wedge
• screw
• wheel and axel
• inclined plane

Building Science Concepts Book 59 Levers, Friction, and Motion lists the following idea and concepts:

Big idea:
Levers change forces in ways that make it easier for work to be done.
Concepts:
Levers can make it easier to move things - they seem to be force magnifiers.
All levers have a point where a force is applied and a point where it is felt.
All levers have a point where they pivot or turn, and this is called their pivot.
A single lever can either move things further or move them with less applied force, depending on its design. It can't do both.
Forces can make objects start moving, speed up or slow down. they can also change the direction of movement.
Many simple levers use length (distance) to make it possible to move things with less applied force.
Some leavers change the direction of a force to create movement in a different direction.

Although we usually think of levers as something in machines, our bodies use a variety of levers. Find out how our bones and muscles act together to form levers in the article on the right.

Use the resource on the right to put learning about our body's levers into action.

A bicycle is a compound machine made up of several simple machines:

• levers - brakes, gear shifters and handle bars
• pulleys - chain on the gears, parts of the shifting and braking mechanisms and the drive train
• inclined plane, wedges and screws - teeth on the chain rings, screws that hold the bike together, the tyre repair kit uses wedge and lever
• wheel and axle - the wheels, pedals and crankset.

Use the image to the right to identify where these simple machines are located and how they have been improved over the years.

The Yike Bike is not a simple machine. In fact, its clever design eliminates a simple machine. Can you figure out which machine is gone?

Read the article on the right to test your knowledge.

A screw is an inclined plane wrapped around a cylinder. Some examples of screws include:

• jar lids
• electric fan blades
• drill bits

Rotating screw blades can move materials. For example: an Archimedes' screw carries water from a low-lying area to a higher spot.

Use the video on the right to see how rotating screw blades move a mixture through a machine.

What other simple machines can you see in the video?

A wedge is a triangular shaped object. It can:

• separate two objects or split an object into portions
• lift an object
• hold an object in place.

When force is applied to the flat end, energy is transported to the pointy end.

A wedge also acts as an inclined plane. When the edge of a blade is pushed into an object, it overcomes the resistance of the material to separate it. Wedges can separate thick or hard materials with less force and a reasonable degree of precision.

Use the article to the right to see how a wedge is used to split firewood safely and precisely.